Many companies wrote their in-house framework for ETL. For example I have worked in two companies that both chose to write sort of YAML based ingestion framework so that users only need to write YAML.

I guess you can make the case that a general framework is useful, but TBH I think either it takes too long to include all use cases (and each company probably only needs one), or becomes too complicated to be a framework.

Not to discourage you though, it's fun to build your own project and I'd love you to try it out. Worst case, no one uses it but you bag a ton of experience.